Enhancement of the liquid feed distribution in gas‐solid fluidized beds by nozzle pulsations (induced by solenoid valve)

In this work, it was found that spray nozzles pulsations greatly improved the liquid feed spray distribution on fluidized bed particles. Pulsating a spray nozzle doubled its nozzle performance index at various operating conditions. The objective of this study was to impose fluctuations of well‐defined frequency and amplitude on the liquid spray to investigate potentially beneficial effects of fluctuations on the liquid feed distribution on the particles in the fluidized bed. Three sets of experiments were conducted to study the quality of the spray jet‐bed interaction using a conductance probe method. The jet penetration for each experiment was calculated theoretically. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Mass transfer in tube bundles with liquid fluidized particles

Experimental studies were conducted of overall and local tube-to-liquid mass transfer for bundles of horizontal tubes in staggered and in-line arrays in a liquid fluidized bed. The mass transfer coefficients are compared with those obtained using a fixed packing and those obtained without particles at the shell-side of the bundle.     

Enhancement of the liquid feed distribution in gas solid fluidised beds by non‐mechanically induced nozzle pulsations

The effect of non‐mechanically induced nozzle pulsations was investigated in the current work, and it was found that appropriately tailored spray nozzles pulsations resulted in the dramatic improvement of the liquid feed spray distribution on particles of a fluidised bed. Non‐mechanically induced pulsations were imposed on the liquid spray, using liquid and gas circuits that favour the development of beneficial pulsations. The resulting effect on liquid dispersion on the fluidised bed particles was determined with a conductance method. © 2013 Canadian Society for Chemical Engineering     

Effect of particle tethering and Scale‐Up on solid–liquid mass transfer in Three‐Phase fluidized beds of light particles

Solid–liquid mass transfer in three‐phase fluidized beds with low‐density particles was studied using a tethered benzoic acid particle dissolution technique. Two columns with air, water and polypropylene cylinders were used for experiments. The solid–liquid mass transfer coefficient was found to increase with column diameter but decrease with tether length. The effect of tethering on solid particle movements was also evaluated using radioactive particle tracking (RPT) technique. RPT showed that tethered particles exhibited slower movements. Statistical analysis suggests that tether lengths 3 times the column radius are sufficient to reduce the effects of tethering.     

Experimental profiles of lateral mixing of feed particles in a three‐dimensional fluidized bed

Solids mixing data of high quality is one of the most crucial steps for quantitative studies, but it is a difficult task to obtain in a fluidized bed especially with a 3D configuration. Therefore a novel sampling technique is developed with bed collapse method, for measuring lateral mixing of feed particles in a 3D fluidized bed. The sampling tool is designed using a “bottom‐to‐top sampling” idea. Its development, configuration and measurement repetition are discussed in detail. The effects of mixing time, fluidizing gas velocity, and particle size of bed material on the tracer distribution are investigated. A quantitative comparison of lateral dispersion coefficient shows that our results agree fairly well with measurements and predictions of correlations for lab‐scale fluidized systems in previous studies. The presented 2D profiles of the lateral mixing can be used to validate fundamental solids mixing models or verifying convenient measurement techniques. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Mixing and segregation in a liquid fluidized bed of particles with different size and density

Experimental studies have been carried out on fluidization of irregular particle mixtures of different size and density. The mixing and segregation phenomena could be interpreted on the basis of the diffusion model of Kennedy and Bretton. The dependence of computed particle dispersion coefficient on liquid velocity, particle density and size has been discussed.     

Modified gas‐perturbed liquid model (GPLM) for minimum fluidization velocity in a two‐phase inverse fluidized bed reactor with Newtonian and non‐Newtonian systems

In the present investigation minimum fluidization velocity, U_mf, in a two‐phase inverse fluidized bed reactor is determined using low‐density polyethylene and polypropylene particles of different diameters (4,6 and 8 mm) by measuring pressure drop. In a glycerol system U_mf decreased gradually with increase in viscosity up to a value of 6.11 mPa s (60%) and on further increase there was a slight increase in U_mf. In the case of the glycerol system the U_mf was found to be higher when compared to water. In the non‐Newtonian system (carboxymethylcellulose), U_mf decreased with increase in concentration in the range of the present study. The U_mf was found to be lower when compared to water as liquid phase. The modified gas‐perturbed liquid model was used to predict the minimum fluidization liquid velocity (U_lmf) for Newtonian and non‐Newtonian systems. Copyright © 2006 Society of Chemical Industry     

Radioactive particle tracking in a lab‐scale conical fluidized bed dryer containing pharmaceutical granule

Radioactive particle tracking (RPT) has been used to study the motion of the particulate phase in a bench‐scale conical fluidized bed containing dried pharmaceutical granule. RPT revealed that there is a distinct circulation pattern of the granule with particles moving upwards at high velocities near the centre of the bed and falling slowly near the walls. There was also a localized region near the centre of the bed where particles moved downward rapidly. The particle size distribution (PSD) of the granule had an appreciable impact on particle motion with a wide PSD leading to larger fluctuations in particle velocity as well as poorer granule mixing.     

Distribution of large biomass particles in a sand‐biomass fluidized bed: Experiments and modeling

The axial distribution of large biomass particles in bubbling fluidized beds comprised of sand and biomass is investigated in this study. The global and local pressure drop profiles are analyzed in mixtures fluidized at superficial gas velocities ranging from 0.2 to 1 m/s. In addition, the radioactive particle tracking technique is used to track the trajectory of a tracer mimicking the behavior of biomass particles in systems consisting of 2, 8, and 16% of biomass mass ratio. The effects of superficial gas velocity and the mixture composition on the mixing/segregation of the bed components are explored by analyzing the circulatory motion of the active tracer. Contrary to low fluidization velocity (U = 0.36 m/s), biomass circulation and distribution are enhanced at U = 0.64 m/s with increasing the load of biomass particles. The axial profile of volume fraction of biomass along the bed is modeled on the basis of the experimental findings. © 2014 American Institute of Chemical Engineers AIChE J, 60: 869–880, 2014     

Impact of a draft tube on industrial‐scale Fluid Coker™ Spray Jets in fluidized beds

In fluidized bed reactors such as Fluid Cokers?, liquid injections are used. Good contact between liquid and bed solids is required to maximize product yields and quality, and gas‐atomized nozzles are, therefore, used in all these processes. The spray nozzle technology is known to affect the liquid distribution. Therefore, the objective of this study is to assess the effect on liquid distribution of a draft tube located downstream of the spray nozzle, inside the fluidized bed. Experiments were conducted at a relevant scale, using a commercial‐scale nozzle with a liquid flow rate of about 100 L/min in a large‐scale pilot fluid bed containing about 7 tonnes of silica sand. Liquid injected into a fluidized bed either forms liquid‐solid agglomerates or free moisture, consisting of individual particles coated with a thin layer of liquid. Several electrodes were used to map the free moisture distribution throughout the bed. A draft tube greatly improves the contact efficiency throughout the bed. It also increases the penetration of the gas‐liquid jet formed by spray inside the fluidized bed.     

Linking micro‐scale predictions of capillary forces to macro‐scale fluidization experiments in humid environments

The effects of increasing relative humidity (RH) on fluidization/defluidization are investigated experimentally and understood via particle‐level predictions for the resulting capillary force. Experimentally, defluidization is found to be more sensitive to small changes in RH than fluidization. This sensitivity is captured by a new defluidization velocity U_df, which characterizes the curvature of the defluidization plot (pressure drop vs. velocity) observed between the fully‐fluidized (constant pressure drop) and packed‐bed (linear pressure drop dependence on velocity) states; this curvature is indicative of a partially‐fluidized state arising from humidity induced cohesion. Plots of U_df vs. RH reveal two key behaviors, namely U_df gradually increases with a relatively constant slope, followed by an abrupt increase at RH ～55%. Furthermore, the bed transitions from Group A to Group C behavior between RH of approximately 60–65%. From a physical standpoint, these macro‐scale trends are explained via a theory for capillary forces that, for the first time, incorporates measured values of particle surface roughness. Specifically, a model for the cohesive energy of rough surfaces in humid environments shows the same qualitative behavior as U_df vs. RH for RH <55%, unlike predictions of the cohesive force. Furthermore, the abrupt transition at RH ～60–65% is explained via the previously observed onset of liquid‐like water adsorption, rather than crystal/ice‐like adsorption, onto glass surfaces. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3585–3597, 2016     

(Gas‐)liquid‐solid circulating fluidized beds and their potential applications to bioreactor engineering

Compared with conventional fluidized beds, circulating fluidized beds have many advantages including better interfacial contacting and reduced backmixing (Lim et al., 1995). While there are many reports on the gas—solid circulating fluidized systems, liquid—solid and gas—liquid—solid circulating fluidized bed systems have been scantily studied. However, extending current knowledge obtained in gas—solid systems to liquid—solids and gas—liquid—solid three‐phase systems is shown to open new horizons for applications of circulating fluidized bed technology and expected to lead to the development of highly efficient liquid—solid and gas—liquid—solid reactors, especially for the ever growing field of biotechnology. In order to fully appreciate the potential of those two types of liquid phase circulating fluidized beds, recent progress is reviewed in this article. Their potential applications to biochemical processes are also discussed.     

Mind the gap: Ensuring laboratory‐scale testing of an electrospinning product meets commercial‐scale needs

Plant & Food BioProcessing has developed a process to electrospin denatured whole‐chain marine collagen. The collagen is routinely tested on laboratory‐scale electrospinning equipment, but when it is electrospun on industrial equipment, the conditions and the product testing criteria differ from those used in the laboratory. A laboratory electrospinning machine was modified to simulate industrial conditions (≥30 kV). Then, several parameters (voltage, working distance) were adjusted from laboratory‐ to commercial‐scale. These changes did not affect average fiber diameter or deposition rate. The optimum electrospinning conditions were a mixture of laboratory‐ and commercial‐scale conditions (30–50 kV; 10 cm working distance). Reducing the working distance by 5 cm improved the production rate by up to 75%. These changes resulted in better repeatability of electrospun fibers over multiple production runs, with fewer adjustments of solutions and parameters. We recommend this approach to design materials and processes relevant to industrial manufacturing of electrospun fibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44836.     

Axial segregation in bubbling gas‐fluidized beds with Gaussian and lognormal distributions of Geldart Group B particles

Bubbling, gas‐fluidized bed experiments involving Geldart Group B particles with continuous‐size distributions have been carried out. Sand of various widths of Gaussian or lognormal distributions were completely fluidized, then axial concentration profiles were obtained from frozen‐bed sectioning. Similar to previous works on binary systems, results show that mean particle diameter decreases with increasing bed height, and that wider Gaussian distributions show increased segregation extents. Surprisingly, however, lognormal distributions exhibit a nonmonotonic segregation trend with respect to distribution widths. In addition, the shape of the local‐size distribution is largely preserved with respect to that of the overall distribution. These findings on the nature of local‐size distribution provide experimental confirmation of previous results for granular and gas‐solid simulations. Lastly, an interesting observation is that although monodisperse Geldart Group D particles cannot be completely fluidized, their presence in lognormal distributions investigated still results in complete fluidization of all particles. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Nonspherical particles in a pseudo‐2D fluidized bed: Experimental study

Fluidization is widely used in industries and has been extensively studied, both experimentally and theoretically, in the past. However, most of these studies focus on spherical particles while in practice granules are rarely spherical. Particle shape can have a significant effect on fluidization characteristics. It is therefore important to study the effect of particle shape on fluidization behavior in detail. In this study, experiments in pseudo‐2D fluidized beds are used to characterize the fluidization of spherocylindrical (rod‐like) Geldart D particles of aspect ratio 4. Pressure drop and optical measurement methods (Digital Image Analysis, Particle Image Velocimetry, Particle Tracking Velocimetry) are employed to measure bed height, particle orientation, particle circulation, stacking, and coordination number. The commonly used correlations to determine the pressure drop across a bed of nonspherical particles are compared to experiments. Experimental observations and measurements have shown that rod‐like particles are prone to interlocking and channeling behavior. Well above the minimum fluidization velocity, vigorous bubbling fluidization is observed, with groups of interlocked particles moving upwards, breaking up, being thrown high in the freeboard region and slowly raining down as dispersed phase. At high flowrates, a circulation pattern develops with particles moving up through the center and down at the walls. Particles tend to orient themselves along the flow direction. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1573–1590, 2018     

Property‐averaging applied to determination of volume contraction in binary‐solid liquid‐fluidized beds

This communication examines experimental information from the literature on the volume contraction that can occur when two monocomponent particle species that have a diameter ratio and a buoyancy‐corrected density ratio on opposite sides of unity are subjected to liquid fluidization as a binary mixture. Attempts are made to predict this volume contraction by applying monocomponent bed expansion equations using averaged properties of the binary solids. It was found that this method works better if the equations are anchored to experimental monocomponent voidages by the fractional bed volume change that they predict than if the equations are used directly. However, greater prediction accuracy can be achieved by correlation of the adjustable parameter G of the Westman, Am Ceramic Soc, 19 , 127–129, (1936) equation, originally applied to binary packed beds.     

Simulations of scalar dispersion in fluidized solid–liquid suspensions

Direct, particle‐resolved simulations of solid–liquid fluidization with the aim of quantifying dispersion have been performed. In addition to simulating the multiphase flow dynamics (that is dealt with by a lattice‐Boltzmann method coupled to an event‐driven hard‐sphere algorithm), a transport equation of a passive scalar in the liquid phase has been solved by means of a finite‐volume approach. The spreading of the scalar—as a consequence of the motion of the fluidized, monosized spherical particles that agitate the liquid—is quantified through dispersion coefficients. Particle self‐diffusivities have also been determined. Solids volume fractions were in the range 0.2–0.5, whereas single‐sphere settling Reynolds numbers varied between approximately 3 and 20. The dispersion processes are highly anisotropic with lateral spreading much slower (by one order of magnitude) than vertical spreading. Scalar dispersion coefficients are of the same order of magnitude as particle self‐diffusivities. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1880–1890, 2014     

An evaluation of the solid hold‐up distribution in a fluidized bed of nanoparticles using radioactive densitometry and fibre optics

An experimental study was conducted to assess the solid hold‐up distribution in a fluidized bed of zirconia and aluminum nanoparticles. For this purpose, two different techniques, radioactive densitometry and fibre optic measurement, were used. The results showed that while the fluidization of these nanoparticles occurs in the agglomeration state, it performs homogeneously in terms of phase concentration. This matter is important especially when a polymerization reaction should take place uniformly on the surface of nanoparticles, where the monomer is the fluidizing gas. Both techniques presented uniform solid hold‐up distribution over the cross‐section, although the fibre optic method overestimated the overall solid concentration, which was obtained based on bed expansion results. The radioactive densitometry was, however, capable of properly predicting the phase concentration within the bed according to the bed expansion observation. Finally, the effect of bulk density on the fluidization of nanoparticles was discussed by comparing the fluidization of different types of particulate materials.